Life below the surface

By Abby Anthony

Beginning this summer, the U.S. Environmental Protection Agency and Dr. John King of the University of Rhode Island's Graduate School of Oceanography are using a new technology called sediment profiling imagery to obtain pictures of the organisms and sediment on the sea floor.

Last Tuesday, Aug. 8, Stephen Johnson, the new administrator of the EPA appointed by President Bush in 2005, visited Allen's Harbor in North Kingstown to learn more about sediment profiling imagery and how it might change coastal science and policy.

In the benthic zone

Just above the sediment surface on the ocean floor is an area known as the benthic zone. Organisms living in this zone are called benthic organisms, and are accustomed to cooler temperatures, low levels of light, and may have a high tolerance for low levels of oxygen.

The most important of the benthic organisms are the millions of bacteria living within the sediment. Bacteria are involved in the cycling of organic matter in the sea, consuming oxygen all the time. With greater amounts of organic matter, like decaying algae, more oxygen is consumed, sometimes leaving the bottom waters dangerously low in vital oxygen.

Other benthic organisms - such as worms, quahogs, scallops, and fish - also require oxygen to live. If these organisms cannot swim to a new location with more oxygen, they may not be able to survive if conditions persist. Understanding this benthic ecosystem is especially important in Narragansett Bay, where very low dissolved oxygen levels have caused marine life to die en masse in recent years.

A hard to study ecosystem

Historically, scientists' understanding of life below the ocean floor has relied upon destructive sampling techniques. To observe benthic sediment and organisms, scientists had to scoop up samples of the sediment and sift through the mud. While these studies are an important step in understanding the benthic ecosystem, advances in knowledge have been limited by two main factors.

First, the ocean floor is not very accessible. Scientists need boats and special equipment to take samples from the bottom. Second, without being able to see the environment below the ocean floor, it is very hard for scientists to understand the structure and patterns of the benthic ecosystem. Scientists' perceptions of what exists beneath the ocean floor have been limited by the sampling methods.

In recent years, scientists have made substantial leaps in their understanding of benthic ecosystems by using new technology - cameras that can take photographs of the sediment below the ocean floor.

New technology

Originally designed by Dr. Joseph Germano and Dr. Donald Rhoads, a sediment profiling imager consists of two main parts, a digital camera and a prism. The digital camera is encased in a pressurized housing and the prism has a clear Plexiglass faceplate and a mirror to reflect the image of the sediment into the camera lens. The bottom edge of the prism is sharpened so that it can cut through the sediment, and the lens and light source used to illuminate

the sediment are contained within the prism. The digital camera is focused on the Plexiglass faceplate and records the sediment and benthic organisms that are pressed against the faceplate. This configuration allows the camera to work in complete darkness and still take high-resolution images.

When SPI technology was first developed, it was often used to track contaminated dredging sediment. Contaminated sediment is often dumped on the ocean floor and then capped with clean sand, and SPI was used to determine how the contaminated sediment was dispersed over time. As the technology's potential for quickly assessing environmental conditions was realized, SPI was used to map benthic areas of low dissolved oxygen, map coastal and off-shore benthic habitats, and examine sediment quality.

This summer King and his research assistants have been using SPI technology to take photographs of the sediment in Greenwich Bay. The researchers are looking at the photographs for indicators of low levels of dissolved oxygen. The absence of worms, shellfish, and lady slippers might indicate that there is not enough oxygen for marine life to survive in the sediment. The information that King obtains through SPI technology will eventually be used to help determine the cause of low dissolved oxygen levels, direct remediation actions and coastal management plans, and enhance the health of Narragansett Bay.

Special thanks to EmilyShumchenia and Erika Lentz fromthe Graduate School ofOceanography at URI.